Flavour Biosynthesis Pathways in Grape Cell Cultures: Sesquiterpenes Biosynthesis

The aim of this study was to discover genes involved in grape flavour pathways by elicitation of grape cell suspension. Among numerous elicitors tested, methyl jasmonate (MeJA) and jasmonic acid (JA) induce a wide range of sesquiterpenes in 'Cabernet Sauvignon' and 'Riesling' berry cell suspension cultures. Sesquiterpenes, the largest subclass of natural terpenes compounds, may be synthesised by two different pathways: the mevalonate pathways (MVA) localised in the cytosol and the methylerytritol phosphate pathway (DOXP/MEP) localised in the plastids. Using specific inhibitors we found that in our cell suspension MeJA induced sequiterpenes are synthesised by the MVA pathway. A set of experiments performed to optimize sesquiterpenes production, indicated that the efficacy of MeJA concentration is strictly dependent upon the density of cells in cell suspension at the moment of elicitor addition. In time course studies, it was found that the peak in sesquiterpene accumulation was recorded 72 hours after MeJA addition. For the time-course experiment, we analysed the expression of ten terpene synthase homologues found in the grape EST database by real-time RT-PCR. The expression of at least four of these putative sesquiterpenes synthase genes are induced by MeJA, with maximum expression at 24 hours, therefore, 48 hours before the peak of sesquiterpene accumulation.